As some users asked me about this and there is also a bug on Bugzilla, I think it is a good idea to write a short explanation about this change in 6.2.
Some versions ago, I decided to move "API-like functions" to the global goPrefBar context, so only one instance is held in memory for one Firefox/SeaMonkey session.
For a few versions, I kept backwards compatibility, but in 6.2, I dropped this, so "prefbarExecute" finally was dropped from the PrefBar codebase.
The replacement is "goPrefBar.RunApplication". It can be used just like the old "prefbarExecute". You may still create an array of arguments and just pass it to the function as second parameter. But you no longer have to do it that way. It's also possible to add the arguments directly to "goPrefBar.RunApplication" like this:
goPrefBar.RunApplication("/usr/bin/konsole", "--hold", "-e", "echo", "test");